B58 Catless Downpipe: Performance Gains, Sound, and Install Overview

$200, a $22 gasket and an afternoon on jack stands is what separates a Stage 1 B58 from a Stage 2 B58. The factory downpipe bolts to the turbine housing and carries the primary catalytic converter, so it is the biggest restriction left in the exhaust once the car is tuned. The OneFastShop B58 4.5 inch catless downpipe removes it.

This guide decides whether a B58 catless downpipe is the right buy for your F22 M240i, G20 M340i, G30 540i or A90 Supra: what it adds on 93 octane, how it sounds and smells, which years it fits, how the install goes, and how it compares with catted pipes from Active Autowerke, AMS and MST and with the stock part.

One limitation up front: this is a competition part. It will not pass an emissions inspection, it smells at idle, and it needs a tune to be worth doing. Facts come from our product page, the makers' pages, and owner threads on SupraMKV and Bimmerpost.

Shop the B58 4.5 Inch Catless Downpipe

The Short Answer

A B58 catless downpipe with a supporting Stage 2 tune is worth 30 to 40 horsepower over a stock car on 93 octane, with earlier spool and lower exhaust temperatures. The $199.99 OneFastShop pipe fits 2016 to 2024 B58 BMWs and the 2020 to 2024 Supra 3.0. It is off road and competition use only, it smells at idle, and it needs a tune with the rear O2 off.

At a Glance

What a B58 Catless Downpipe Changes

A B58 catless downpipe replaces the factory pipe and its built in catalytic converter with an open 4.5 inch tube, so exhaust leaves the turbine with far less back pressure. On a tuned car that does three things.

• The turbo spools sooner. Boost arrives earlier, in the 2,500 to 4,000 rpm band you actually drive in.
• Exhaust gas temperatures drop. The map can run more timing and boost before it pulls back for heat.
• The tune can ask for more. A Stage 2 map targets higher boost than Stage 1 because the restriction is gone. The pipe opens the door; the map walks through it.

Without a tune the car gains very little and sets a catalyst efficiency code, usually P0420. A 2024 Supra owner on SupraMKV who fitted a 5 inch catless pipe on the stock map also had the car overboosting and closing the throttle until it was flashed. Plan the pipe and the map as one job.

Real Gains on 93 Octane: 30 to 40 Horsepower With a Tune

Expect 30 to 40 horsepower over stock from the downpipe with a supporting Stage 2 tune on 93 octane, with a similar torque gain lower in the revs. bootmod3's gain tables put Gen 1 Stage 1 on 93 at about 20 percent over stock and Stage 2 at about 26 percent, so the pipe and the map together are where the big number comes from.

Owner numbers agree. A 2021 Supra 3.0 on SupraMKV with a catless pipe, stock intake and a Stage 2 map on 93 octane put down 443 whp and 522 wtq, and his own back to back baseline showed close to 20 whp from the pipe alone. That lines up with the 30 to 40 horsepower we quote with a supporting tune, because the map does the rest of the work once the restriction is gone.

Not sure which map your car should be on? Read B58 Stage 1 vs Stage 2: Which Do You Need? and bootmod3 vs MHD before you buy either.

What It Sounds Like, Including the Smell

A B58 catless downpipe on the factory exhaust is close to stock at idle and cruise in Comfort, noticeably louder and raspier under load, and much louder in Sport with the valves open. The catalytic converter is also a muffler, so removing it adds volume, turbo whistle and more pops on the overrun.

Owners on SupraMKV split on rasp: one on the stock cat back called it "kinda raspy," while a 2021 Supra 3.0 owner on an FI Exhaust catless pipe reported little to none and minor cabin noise above 30 mph unless at full throttle. A 2024 Supra manual owner measured 73 to 74 dB at idle in Normal and 75 to 76 dB in Sport on a 5 inch catless pipe. None of them reported drone on the factory exhaust. Drone shows up when a catless pipe meets a non resonated aftermarket cat back, so keep a resonated or valved rear section on a highway car.

The smell is the part people underestimate. Every catless owner thread we read mentions it: a rich fuel smell at idle, in the garage and on cold starts. Ethanol softens it, a tune does not remove it, and only a catalytic converter gets rid of it. If you park in an attached garage, this matters more than the sound.

Fitment by Chassis and Year

The OneFastShop B58 catless downpipe fits the Gen 1, Gen 2 (B58TU) and 48 volt mild hybrid B58 on the factory turbo flange, clamp and mount. It does not fit the third generation B58. The table below is the fitment list from our product page.

Gen 1 and Gen 2 cars share the turbo flange, so the pipe is the same. Fueling is what changes: the Gen 1 high pressure fuel pump is the first limit, around E30, while Gen 2 cars run 350 bar injection and take more ethanol before they need pump work. Euro and other OPF market cars built from mid 2018 carry a gasoline particulate filter behind the downpipe and need an OPF specific pipe. Unsure of your build? Send us your VIN and we will confirm fitment before you order.

Catless vs Catted vs Stock: How the Options Compare

A catless pipe wins on price, sound and exhaust temperature; a high flow catted pipe wins on smell and resale; the stock downpipe wins on warranty and legality and loses on everything else. Prices are list prices from each maker and vary by dealer.

The honest read: no catted B58 pipe we know of carries a CARB EO, so even the GESI options are 49 state parts. If you want the cleanest, most reversible setup, keep the factory pipe and buy a cat back; our downpipe vs cat back guide walks through that choice.

Installing a B58 Catless Downpipe

Installing a B58 catless downpipe takes a capable DIYer 2 to 4 hours on jack stands, needs no cutting or welding, and comes down to one V band clamp at the turbo, one joint at the mid pipe, the oxygen sensors and the heat shields in the way. All wheel drive cars have less room next to the front driveshaft, so budget the long end.

1. Soak the V band nut, mid pipe joint and O2 sensors in penetrating oil the night before. They live in the hottest spot on the car.
2. Raise the car, pull the underbody panels and the downpipe heat shields. Keep the shield bolts sorted.
3. Unplug and remove the oxygen sensors with a 22 mm O2 socket.
4. Loosen the turbo V band and the rear joint. BMWs use a clamped joint at the mid pipe; the Supra is a slip fit. One SupraMKV owner found loosening the nut just downstream gave enough flex to walk the old pipe out; another gave up after 30 minutes and dropped the cat back. Both work.
5. Seat the new 4.5 inch crush gasket on the turbo flange, hang the pipe, and snug the clamps loosely so it can still rotate.
6. Bolt the bracket, check clearance, then torque. Look for contact at the subframe, steering shaft and body, then tighten the V band and clamps to the factory spec in BMW TIS. Our product page does not publish a torque value, so do not guess; an over tightened V band cracks.
7. Refit sensors and shields, then flash. Anti seize on the sensor threads, start the car, listen at the flange for a tick, flash the Stage 2 map before any hard driving, and recheck the clamps after a few heat cycles.

Shops book it as two to three hours of labor. Pipe, gasket and map together put a DIY Stage 2 on 93 octane around $660 to $820 depending on whether you flash with MHD or bootmod3.

What Owners Actually Say

Owner threads on a B58 catless downpipe agree on the power and split hard on whether the smell is livable. Here are five, including the one who went back to a cat.

• 2021 Supra 3.0, catless pipe, Stage 2, 93 octane (SupraMKV). 443 whp and 522 wtq on a stock intake, close to 20 whp from the pipe alone back to back. Happy.
• 2021 Supra 3.0 Premium, FI Exhaust catless, MHD Stage 2 on E40 (SupraMKV). Louder but reasonable on the stock cat back, far louder in a garage and on cold start, little rasp, idle smell that ethanol softens. An occasional code when driven hard cold cleared once warm. Mixed, keeping it.
• 2020 M340i, catless pipe, Pure900 turbo (G20 Bimmerpost). Tired of the fuel smell and pricing a GESI catted pipe instead, while worrying the cat will not survive the turbo. Negative.
• 2024 Supra manual, 5 inch catless, stock map at first (SupraMKV). Quiet at 73 to 74 dB idle and no code after 30 minutes, but overboosting and cutting throttle until tuned. Smell worse than expected but tolerable.

The one who took it back off. A MK5 Supra owner on SupraMKV installed a catless downpipe and pulled it months later because he could not handle the smell, then asked whether a tune would fix it. A 2020 Supra owner who had run an aFe catted pipe and then an AMS catless pipe with a tune answered that the smell was nonexistent catted and strong catless, and "a tune won't fix that." He was right. The only fix is a catalytic converter.

Our own pipe gets the same scrutiny. We have no forum reports of cracked welds or bracket failures on it; if one appears we will add it here.

Legal and Emissions

This part is sold for off road and competition use only. Removing or defeating a catalytic converter on a vehicle driven on public roads violates the Clean Air Act, and many states inspect for it. Check your state and local laws before buying.

A catted alternative is sold as emissions legal for your state only when it carries a CARB Executive Order or EPA verification, and we are not aware of a B58 downpipe with a CARB EO. The Active Autowerke and AMS GESI pipes are sold as EPA registered 49 state parts and both makers exclude California. A catless pipe also sets a P0420 code on a stock map, and a dealer can deny a related warranty claim once they see one. Keep the factory downpipe.

Competition parts are returnable unused under our return policy. Street legality is not a return reason, so decide before you order.

Mistakes We See

• Installing it on a stock map and waiting to see. You get a P0420 code, possible overboost cuts, and almost none of the power. Buy the map first.
• Reusing the crush gasket. The OE 18328612538 ring is single use. A reused one ticks at the flange and leaks past the upstream sensor, which skews the tune.
• Trusting the sport display. A Supra owner on SupraMKV read 475 hp on the dash before and after his downpipe and asked what was wrong with the car. The gauge is an estimate. Only a dyno, same session and same fuel, tells you what the pipe did.
• Pairing it with a non resonated cat back on a highway car. That is where drone comes from. Keep a resonated or valved rear section if you live at 70 mph.
• Ignoring the fuel system on a Gen 1 car. The factory high pressure pump on 2016 to 2019 cars runs out around E30. Stage 2 on 93 is fine; Stage 2 on E50 is not without pump work.
• Throwing away the stock downpipe. You will want it for an inspection, a dealer visit or the sale. Store it.

Who This Is For (and Who Should Skip It)

This pipe is for the B58 owner who runs or is about to run a Stage 2 map, uses the car off road or in competition, has no inspection to pass, and is fine with a louder, raspier car that smells rich at idle. For that buyer it is the cheapest meaningful power on the engine.

Skip it if the car is your only daily and lives in an attached garage, if you are in an inspection state and keeping the car registered there, if the car is under factory warranty and you want every claim clean, or if you want more sound without more power. The first three should look at a GESI catted pipe or stay stock; the last one wants a cat back.

If It Were Our Car

On a Gen 1 car such as an F22 M240i or F30 340i: catless pipe, 4.5 inch gasket, Stage 2 on 93 octane, and stop there until the fuel system is upgraded. The Gen 1 HPFP is the wall at about E30.

On a Gen 2 car such as a G20 M340i or a 2021 to 2024 Supra 3.0: catless pipe and a Stage 2 E30 to E50 flex fuel map, because the 350 bar fuel system can use it. That is the combination behind the 443 whp Supra above, and the one we would pick.

On a daily in an inspection state: we would not install this pipe. We would run the AMS or Active Autowerke GESI pipe with a Stage 2 map and accept the cost and the small loss in sound. The only place we hedge is California, where no B58 downpipe we know of is legal, catted or not.

What It Pairs With

A B58 catless downpipe needs two things on day one and two more as power climbs. We are an authorized dealer for every brand we carry, and in stock hardware ships fast. Our pipe ships free to the lower 48 states, and we ship worldwide with shipping calculated at checkout.

• A Stage 2 map. MHD or bootmod3, rear O2 off. We sell parts, not tunes; the bootmod3 vs MHD guide lays out the costs neutrally.
• The 4.5 inch turbo gasket. Our B58 turbo to downpipe gasket is the OE 18328612538 crush ring, $21.99, one per car.
• The rest of the exhaust. The pipe works with the factory cat back and aftermarket systems. Our exhaust, muffler and tip collection has AWE, Akrapovic and Dinan rear sections for the M240i, M340i and Supra; the downpipes collection has the S55 and S58 versions of this pipe.
• Fuel, when ethanol comes in. Gen 1 cars hit the HPFP limit around E30, and higher blends or a bigger turbo call for a low pressure pump too. See our B58 LPFP guide.
• Cooling, when you lap it. More boost means more heat soak; our B58 cooling upgrades guide covers heat exchangers and charge coolers.

Planning the whole car? The B58 bolt-on build guide puts these in order. Driving an M car? See our S55 and S58 downpipe guides. House brand parts carry a 1 year warranty; details are on our warranty page.

Check Fitment and Order the B58 Downpipe

The Bottom Line

A B58 catless downpipe is the cheapest real power on the engine: $199.99 for the pipe, $21.99 for the gasket, and 30 to 40 horsepower over stock with a supporting Stage 2 tune on 93 octane. The turbo spools sooner, exhaust temperatures drop, and the car gets louder and raspier under load while staying near stock in Comfort. It also smells rich at idle, sets a code without a tune, and is sold for off road and competition use only. Gen 1 cars stop at E30 until the HPFP is addressed; Gen 2 cars can go straight to a flex fuel map. If you need to pass an inspection, a GESI catted pipe from AMS or Active Autowerke is the 49 state answer, and the factory pipe is the only answer in California.

Frequently Asked Questions

How much horsepower does a B58 catless downpipe add?

About 30 to 40 horsepower over stock with a supporting Stage 2 tune on 93 octane, with more on E30 to E50 blends. One 2021 Supra 3.0 owner measured close to 20 whp from the pipe alone on the same Stage 2 map, with the map making up the rest.

Do I need a tune for a B58 downpipe?

Yes. The Stage 2 map is where most of the power comes from, and it turns off the rear oxygen sensor so the car does not set a P0420 catalyst code. On a stock map you get a code, possible overboost cuts and almost no gain.

Is a catless B58 downpipe street legal?

No. This part is sold for off road and competition use only. Removing or defeating a catalytic converter on a vehicle driven on public roads violates the Clean Air Act, and many states inspect for it. Check your state and local laws before buying.

Does a B58 catless downpipe drone or sound raspy?

On the factory exhaust, owners report little drone and a raspier note under load that stays near stock in Comfort. Drone shows up when a catless pipe is paired with a non resonated aftermarket cat back, so keep a resonated or valved rear section on a highway car.

Will a catless downpipe make my B58 smell?

Yes. Every catless owner thread we read reports a rich fuel smell at idle, in the garage and on cold starts. Ethanol blends soften it, a tune does not remove it, and only a catalytic converter eliminates it.

Which B58 cars does the OneFastShop downpipe fit?

Single turbo B58 BMWs from 2016 to 2024, including the F22 M240i, F30 340i, F32 440i, G20 M340i, G22 M440i, G30 540i, G01 X3 M40i, G05 X5 40i and G29 Z4 M40i, plus the 2020 to 2024 GR Supra 3.0. OPF market cars and the third generation B58 need a different pipe.

Do I need a new gasket for the install?

Yes. The turbo flange uses a single use 4.5 inch crush gasket, BMW OE 18328612538, which is not in the box. Order one per car with the pipe and do not reuse the old one.